Growth of biomass

ABSTRACT

This invention provides apparatus for the growth of biomass from a supply of suitable nutrient wherein the volume of biomass and the size and shape of the units in which it is present within a vessel (10) in which the reaction takes place can be accurately controlled. Control is achieved by providing a support structure (14) for the biomass comprising one or more movable bodies each of which has an internal reticular structure defining a substantial voidage therein and which essentially fills with the biomass but which does not overfill since excess growth is restricted. Restriction can be achieved by removal of excess biomass or by removal of the bodies at the time that they become filled. The techniques are capable of numerous industrial applications including various biological fermentation processes as well as the purification of sewage and industrial effluents, for example.

This is a continuation of application Ser. No. 513,436 filed July 13,1983, U.S. Pat. No. 4,498,985, which is a continuation of applicationSer. No. 347,872 filed Feb. 11, 1982, U.S. Pat. No. 4,419,243 which is acontinuation-in-part of application Ser. No. 156,038 filed June 3, 1980,abandoned, which is a division of application Ser. No. 945,869 filedSept. 26, 1978, abandoned.

This invention concerns apparatus for use in growing biomass from asupply of suitable nutrient.

Examples of processes with which the invention is concerned and whichare practised industrially are biological fermentation processes ofvarious kinds and the treatment of sewage or industrial effluent by theso-called activated sludge process to reduce the BOD of the effluent.

The present invention is based upon an appreciation of the possibilityof providing biomass within a reaction vessel such that the volume ofbiomass present is accurately known and is present in packages of knownsize and form. In this way the concentration of biomass can be sustainedat an optimum level and the age of the biomass and therefore the overallyield from reactions, as well as the nature of those reactionsthemselves, can be determined and controlled.

According to the present invention, there is provided apparatus for usein a process wherein biomass is grown from a supply of suitable nutrientmaterial, comprising the steps of providing a vessel in which iscontained a biomass support medium in the form of at least one movablebody having an internal substantially uniform reticular structuredefining an internal voidage consisting of a multiplicity ofinter-connected pores such as to provide therein a protectiveenvironment which will permit biomass growth therewithin and thussupport and contain biomass as a substantially integral mass within saidvoidage, the protective environment thus provided allowing the or eachbody to essentially fill with biomass over a period of time, there beingan extensive area of access from the external surface of the or eachsaid body to the whole of the voidage therein; causing the nutrient andany additional substances required for the process to contact and enterthe support medium within the vessel; and causing movement of thesupport medium within the vessel during the growth process sufficientlyfor restricting accumulation of biomass outwardly from the outer surfaceof the or each said body and thus preventing overfill of biomass ontothe outer surface of the or each said body.

The restriction of such outward accumulation can be achieved bycontinual or periodic removal of such biomass or by removal of the bodyor bodies from the vessel before such outward growth occurs.

Preferably the voidage within the internal structure of each said bodyis such that the biomass supported by and contained within said body ispresent as an integral mass.

In one preferred form of apparatus for carrying out the process there isprovided a reaction vessel which contains a multiplicity of said bodies,each of which:

(a) is of such shape as to enable the bodies to move relative to oneanother with a rubbing and/or knocking action without packing togetheras a solid unit;

(b) has an outer surface of such character that the bodies do notinterlock with one another during such relative movement;

(c) has substantial voidage within its internal structure; and

(d) has an extensive area of access from its outer surface to suchvoidage.

The apparatus further includes means for passing fluid containing thenutrient material and other substances necessary to suppoort thereaction through the vessel under such conditions that there is somemovement of the individual bodies relative to one another such anybiomass which tends to grow outwardly from the outer surfaces thereof isreleased through attrition.

In an alternative preferred form of apparatus for carrying out theprocess there is provided a reaction vessel containing a multiplicity ofsaid bodies each of which:

(a) has an outer surface of such character that the bodies do notinterlock with one another during relative movement;

(b) has substantial voidage within its internal structure; and

(c) has an extensive area of access from its outer surface to suchvoidage.

The apparatus further includes means for introducing said bodies free orsubstantially free of biomass to the vessel and means for removingbodies supporting and substantially filled with biomass from the vessel,the residence time of bodies in the vessel being such that they areremoved before growth of biomass outwardly from their outer surfaces canoccur.

The invention will be further apparent from the following descriptionwith reference to the several figures of the accompanying drawings whichshow, by way of example only, two forms of apparatus for the treatmentof sewage effluent by the so-called activated sludge treatment processand embodying the invention.

Of the drawings:

FIG. 1 shows a partially cut-away side elevation of the first form ofapparatus;

FIG. 2 shows a partially cut-away side elevation of the second form ofapparatus;

FIG. 3 shows a perspective view of one of the bodies of the apparatus ofFIG. 1 or FIG. 2 and on an enlarged scale; and

FIG. 4 shows a perspective view of an alternative form of body for theapparatus of FIG. 1 or FIG. 2, again on an enlarged scale.

In the conventional activated sludge treatment process, sewage orindustrial effluent is aerated and agitated within a vessel in thepresence of a biological population which metabolises on variousimpurities contained within the effluent and grows to produce so-calledsecondary sludge which can be removed from the effluent bysedimentation. The concentration of biological population within thetreatment vessel will vary with changes in composition of effluent,residence time and numerous other factors but will in any event belimited with the result that the treatment vessel will need to be muchlarger than would be necessary if higher concentrations of biologicalpopulation could be sustained.

Referring now to FIGS. 1 and 3 of the drawings, it will be seen that thefirst form of apparatus is essentially comprised by a verticallyextending cylindrical column forming a reaction vessel generallyindicated at 10. The vessel 10 is closed adjacent its lower and upperends by perforate plates 11 and 12 respectively. The space between theplates 11 and 12 is partially filled with a multiplicity of bodies 14whose structure will be described in greater detail hereinafter. Each ofthe bodies 14 however supports and contains biomass forming part of thetotal biological population contained within the vessel 10.

Effluent, in this case sewage effluent derived from raw sewage afterscreening and, if required, primary sedimentation thereof, is passedupwardly through the vessel 10 by introduction through the line 15 to achamber 16 located beneath the plate 11. Liquid leaves the upper end ofthe vessel 10 by passage through the apertures in the plate 12 tooverflow into a collecting main or gutter 17 which is connected by aline 18 to the chamber 16 by way of a pump 19 which serves to recycle aportion of the liquid, excess liquid (equal to the inflow through line15) being led away through the line 20 on the pressure side of the pump19.

Air is supplied separately to the chamber 16 from a compressor 22 via aline 23.

As the effluent and air flow upwardly through the vessel 10 they reactwith the biological population supported and contained with the bodies14 causing breakdown of various substances including carbonaceous andproteinaceous materials to produce carbon dioxide and additionalbiomass.

The bodies 14 do not pack the space between the plates 11 and 12tightly, whereby the flow of gas and liquid through the vessel 10 causessome movement of the bodies 14 relative to one another within the bed.This movement is such as to cause the outer surfaces of the bodies 14 torub and/or knock against one another, thus causing them to shed throughattrition any excess biomass which tends to build up on their outersurfaces. Contact of the bodies with the walls of the vessel 10 and theflow of liquid over the bodies can also contribute to the release ofexcess biomass.

We have found that the concentration of biomass per unit volume of thereaction vessel utilising bodies of the kind with which we are hereconcerned can be greater by a factor of up to 5 than the concentrationof biomass in a convention aeration tank with the result that thecapacity of the treatment vessel for a given through flow of effluentcan be approximately 1/5 of that of the conventional vessel with aconsequent and substantial reduction in the capital cost of a treatmentplant, assuming equal biomass activity in both situations.

The bodies 14 are of special construction. Their overall shape ispreferably generally rounded or sufficiently so to enable them to moverelative to each other with a rubbing and/or knocking action withoutpacking together as a solid unit. Again, the outer surfaces of thebodies are of such character that they do not interlock with one anotherduring such relative movement. Each of the bodies has an internal,substantially uniform reticular structure defining an internal voidageconsisting of a multiplicity of interconnected pores making up acontinuous voidage. The pore size whioch is substantially constantthroughout is in the region of 0.3 mm to 1 mm in diameter, and optimumresults are achieved at or close to 0.8 mm diameter. Thus their bulkdensity in air is substantially less than the density of the materialfrom which they are formed. Each body has an extensive area of access tosaid voidage from its outer surface as by way of a multiplicity of saidpores which are exposed at said surface. The internal voidage provides aprotective environment which will permit biomasss growth therewithin,and the volume of biomass supported and contained by each body isgenerally present as an integral mass or monolithic structure reinforcedby the reticule within the body.

The bodies can be made from metal such as stainless steel, certainsynthetic plastics, glass or other non-corrodible materials. The bodiesmay be substantially rigid or of sponge-like construction as provided byreticular foam which has been blown during production to remove the cellwalls, leaving only a filamentous structure.

Various modifications are possible. For example, the reaction vessel maycontain bodies of different size which will classify within the bed.Such different sized bodies might support different kinds of organismwhereby different kinds of reaction may take place in the reactionvessel simultaneously.

Referring now to FIGS. 2 and 3 of the drawings, it will be seen that thesecond form of apparatus is essentially comprised by a verticallyextending cylindrical column forming a reaction vessel generallyindicated at 50. The upper end of the vessel 50 is closed by a perforateplate 51 and surrounded by a collecting main or gutter 52 whose functionwill be apparent hereinafter.

The vessel 50 contains a multiplicity of bodies 14, each of which isadapted to support and contain biomass forming part of the biologicalpopulation contained within the vessel 50. The bodies 14 are similar tothose described in connection with the apparatus of FIG. 1, and formedfrom a material which is less dense than water.

A duct 53 communicates with the interior of the vessel 50 adjacent itsupper end, and serves to supply the bodies 14, free of biomass orsubstantially so, into the vessel 50.

Sewage effluent derived from raw sewage after screening, and, ifrequired, primary sedimentation is introduced into the base of thevessel 50 through a line 54 together with air which is supplied from acompressor 55 into the vessel by way of diffusers 56.

As the effluent liquor and air pass upwardly through the vessel 50various impurities, such as carbonaceous and proteinaceous material,contained within the effluent liquor, are metabolised by the biologicalpopulation contained within the vessel 50.

The effluent liquor leaves the top of the vessel 50 through theperforations in the plate 51 to be collected in the main or gutter 52.The majority of the liquor flowing into the main or gutter 52 isrecycled by means of a pump 57 to a line 58 for reintroduction to thevessel 50 at the base thereof. A smaller portion, equal to the feedthrough the line 54 is led off for further treatment through line 59.

Bodies 14 are removed from the vessel adjacent the base thereof throughline 60 together with some of the effluent liquor. The mixture of bodies14 and effluent liquor are passed to a straining device 61 which passesthe liquor through line 62 to the suction side of the pump 57 and theseparated bodies through line 63 to a machine 64 which separates biomasssupported by and contained within the bodies from the bodies themselves.The separated biomass is removed through line 65 as secondary sludge,whilst the bodies 14 freed of biomass are passed through line 66 forsupply to the duct 53.

It will be understood that the bodies are continuously recycled throughthe vessel 50. As the bodies 14 move downwardly through the vessel theygradually support and contain progressively more biomass, eitherbecoming seeded with biomasss contained within the recycling effluentliquor or being seeded by virtue of incomplete removal of biomass in themachine 64.

The apparatus is designed so that the residence time of the bodieswithin the vessel 50 is such that they are removed when they aresubstantially filled with biomass but before biomass can commence togrow outwardly from their outer surfaces.

The machine 64 may separate biomass from the bodies 14 by compression,intense vibration or other mechanical method. As an alternative, thebodies 14 may be freed of biomass for re-use, by a chemical orbiological method such as extended aeration, for example.

The flow of liquor and air through the vessel 50 is such as to fluidisethe bed of bodies 14 sufficiently to enable the bodies 14 to classifywithin the bed so that the apparatus operates in the manner described.

As with the first form of apparatus described, the concentration ofbiomass per unit volume of reaction vessel can be significantly greaterthan possible with conventional activated sludge processes.

Furthermore, the surplus recovered biomass will contain a smallerproportion of free (that is to say extra-cellular) water thanconventional secondary sludges rendering dewatering to a combustiblestate more easy.

Various modifications are possible.

Thus, for example, if the bodies are made from a non-combustiblematerial the biomass contained therein may be removed by combustion.Equally if the bodies are formed from a combustible material they may beburned with the included biomass, fresh bodies being suppliedcontinually instead of recycling a given quantity thereof.

Again, for example, the bodies may be formed from a material more densethan water and passed through the vessel in the opposite direction, thatis from bottom to top.

It will be understood that in both forms of apparatus described thequantity of biomass present in the reaction vessel at any time isreasonably accurately known as is the size and shape of the units orpackages in which it is present and that control of the reaction canthus be more precise and predictable than has been possible hithertowith conventional apparatus.

Various interesting possibilities exist. For example, in either of theforms of apparatus described the bodies may be of such size that asufficiently large volume of biomass is supported and contained wherebyessentially aerobic processes take place at the surface of each body andwithin an internal layer adjacent such surface whilst essentiallyanaerobic processes such as the conversion of nitrates to nitrogen gasoccur in the interior of the body in the deeper layers of biomass.

It must be understood that the size of body necessary to ensure thatboth aerobic and anaerobic processes take place will be dependent uponthe dissolved oxygen level within the reaction vessel. It follows thatthe size of the body can be selected for a given dissolved oxygen levelor the dissolved oxygen level can be adjusted for a given body size togive the desired level of both aerobic and anaerobic processes. Normallythe desired level will be that which minimises biomass production.

As an alternative to bodies constructed from foamed plastics, onesuitable body for use in the apparatus described with reference toeither FIG. 1 or FIG. 2 is as illustrated in FIG. 3 and may be made froma single length of plastic monofilament which is knitted to form a pieceof fabric in the form of a cylindrical tube which is then rolled intotoroidal shape. In a typical example the toroid will have a diameter of5 cm or thereabouts and a thickness of 2 cm or thereabouts.

This body is easily mass-produced and inexpensive and thereforeattractive in applications where large quantities are required as, forexample, in the treatment of sewage or industrial effluent.

Another suitable body is as shown in FIG. 4 and may be made from asingle length of stainless steel wire which is knitted, again to form acylindrical tube, a length of which is compressed into a generallyspherical form. This body is relatively expensive but is more suitablefor applications where bodies of smaller size having a diameter of 0.6cm, for example, are required. Bodies made from stainless steel may beof particular interest where fine chemicals such as pharmaceuticals areto be produced.

It will be appreciated that it is not intended to limit the invention tothe above examples only, many variations, such as might readily occur toone skilled in the art, being possible without departing from the scopethereof.

For example, instead of providing the bodies within a static vesselthrough which the materials to be treated are passed, the bodies may becontained within an open cage-like vessel which is itself moved throughthe materials to be treated. Such a cage-like vessel might take the formof a rotatable drum which is at least partially immersed in a body ofliquid containing materials to be reacted.

Yet again, for example, the bodies may be contained within an opentank-like vessel which is continually stirred with sufficient vigour tocause the bodies to shed excess biomass through liquid shear or byattrition resulting from collision.

Whilst the necessary nutrients will normally be passed over the supportstructure for the biomass, in the form of a liquid together with suchgaseous additives as may be necessary to support the required reactions,there may be applications where the necessary nutrients can be presentin gaseous, mist or vapour form together with sufficient moisture tosustain the biological reaction.

Whilst we have described the invention with reference to the treatmentof effluents, it will be understood that the techniques are applicableto any process wherein biomass is grown from a source of nutrient. Thusthe techniques may be applied to the production of pharmaceuticalsubstances and single cell proteins such as yeast. It is envisaged, forexample, that fermenters used in the brewing and related industriesmight usefully contain the necessary yeast within bodies of the generalkind which we have described.

It will be understood that the bodies, even whilst empty, may serve toact as a filter in the apparatus described with reference to FIG. 2 andin some applications such filtration effect may be advantageous.

What is claimed is:
 1. Apparatus for promoting the growth of biomassfrom a supply of suitable liquid nutrient material, comprising: areaction vessel adapted to contain the liquid nutrient; a biomasssupport medium contained within the vessel and formed as a plurality ofmovable bodies each having a substantially uniform reticular structurethroughout the entire volume of the body, defining an internal voidageconsisting of a multiplicity of interconnected pores such as to providethroughout the body a protective environment which will permit biomassgrowth in said pores and thus support and sustain active biomass as asubstantially integral mass retained by said reticular structure, saidprotective environment thereby allowing each body to fill with biomassover a period of time, there being an extensive area of access by way ofa multiplicity of openings defined by said reticular structure at theexternal surface of each said body, to the whole of the voidage therein,the overall shaped and reticular structure of each body beingsufficiently plain as to enable the bodies to move relative to eachother with a rubbing or knocking action without interlocking or packingtogether as a solid unit; a quantity of liquid nutrient material locatedwithin said reaction vessel; a quantity of biomass located within saidreaction vessel; means for causing the liquid nutrient and anyadditional substances required for the process to flow through thevessel thus to contact and enter the bodies within the vessel; and meansfor causing relative movement of the bodies within the vessel during thegrowth process sufficiently for restricting accumulation of biomassoutwardly from the outer surface of each said body and thus preventingoverfill of biomass onto the external surface of each said body. 2.Apparatus according to claim 1, including means for causing a gaseousmedium to flow over the bodies within the vessel.
 3. Apparatus accordingto claim 1, when used for the treatment of industrial or sewage effluentwhich constitutes the source of liquid nutrient, and including means forintroducing oxygen into the interior of the vessel to meet thebiological oxygen demand.
 4. Apparatus according to claim 1, includingmeans for removing bodies supporting and substantially filled withbiomass from the vessel; means for separating the biomass from thebodies which are removed from the vessel; and means for thereafterreturning said removed bodies to the vessel.